Periodontal disease is the result of the host response to periodontal pathogens such as Porphyromonas gingivalis. P. gingivalis is a black-pigmented, Gram-negative pathogen, which expresses various virulence factors implicated in disease. The overall goal of this project is to define the cellular mechanism(s) involved in the induction of host responses protective against P. gingivalis infection. The studies proposed will concentrate on delineating the mechanisms by which adjuvants modulate host responses to P. gingivalis antigens. Emphasis will be placed on the role of B7 co-stimulatory molecules in host responses and in infection by P. gingivalis, and on the involvement of cytokines, specific target cells, and other cell surface receptors. Specifically, there are plans to: 1) Determine the immunogenicity of the recombinant catalytic domain of the lysine-specific protease Kgp (rKgp-CAT) and the HagA repeat domain (rHArep) of P. gingivalis, and the effect of the B subunit of cholera toxin (CTB) and monophosphoryl lipid A (MPL) in modulating responses to these antigens following intranasal immunization, The level, isotype and IgG subclass of antibodies induced to HArep or Kgp-CAT in serum and external secretion$ will be measured by ELISA. The effects of CTB and MPL in enhancing/shifting responses will be further characterized by measuring antigen-specific proliferation and cytokine production. The effect of the responses, especially the nature of the antibodies, on protection will also be determined. 2) Determine the mechanisms by which the adjuvants CTB and MPL modulate the induction of the immune response. These studies will determine the involvement of the co-stimulatory B7 molecules in the immunoenhancing ability of the adjuvants and in P. gingivalis infection, the target cells affected by the adjuvants and the association between MPL, the Toll-like receptors and B7 co-stimulatory molecules. Groups of mice deficient in B7-l (B7-1-/-), B7-2 (B7-2j or both (B7-1/B7-2-/-) molecules and normal controls will be immunized with HArep or Kgp-CAT with and without CTB or MIPL. The levels of antibody and antibody-secreting cells will be assessed by ELISA and ELISPOT method. The effect of adjuvants on the expression of B7 molecules and of CD4OL will be analyzed by FACS. Differential regulation of cytokines induced and proliferative responses will also be assessed. The involvement of B7 co-stimulation in P. gingivalis infection will be assessed in B7 deficient mice. These studies will provide information on the mechanisms by which mucosal adjuvants modulate host immune responses, the target cells through which their adjuvanticity is exerted and the involvement of co-stimulatory signals provided by B7 molecules and of Toll-like receptors. An understanding of these processes is crucial for the development of means to interrupt/prevent periodontal disease pathogenesis by Porphyromonas gingivalis. Knowledge on the host effects induced by a potential periodontal vaccine will lead to the development of the therapeutic manipulation of effector function leading to the amelioration or prevention of periodontal disease and associated systemic diseases.